package com.yutian.selfservice.support.utils;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;


public class SnowflakeUtils {

    public static final Snowflake snowflake = new Snowflake();

    public static String nextIdStr() {
        return String.valueOf(snowflake.nextId());
    }

    public static long nextId() {
        return snowflake.nextId();
    }
    /**
     * <p>名称：IdWorker.java</p>
     * <p>描述：分布式自增长ID</p>
     * <pre>
     *     Twitter的 Snowflake　JAVA实现方案
     * </pre>
     * 核心代码为其IdWorker这个类实现，其原理结构如下，我分别用一个0表示一位，用—分割开部分的作用：
     * 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
     * 在上面的字符串中，第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，
     * 然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识），
     * 然后12位该毫秒内的当前毫秒内的计数，加起来刚好64位，为一个Long型。
     * 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），
     * 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。
     * <p>
     * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
     *
     *
     */
    private static class Snowflake {
        /**
         * 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
         */
        private final static long twepoch = 1288834974657L;
        /**
         * 机器标识位数
         */
        private final static long workerIdBits = 5L;
        /**
         * 数据中心标识位数
         */
        private final static long datacenterIdBits = 5L;
        /**
         * 机器ID最大值
         */
        private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
        /**
         * 数据中心ID最大值
         */
        private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
        /**
         * 毫秒内自增位
         */
        private final static long sequenceBits = 12L;
        /**
         * 机器ID偏左移12位
         */
        private final static long workerIdShift = sequenceBits;
        /**
         * 数据中心ID左移17位
         */
        private final static long datacenterIdShift = sequenceBits + workerIdBits;
        /**
         * 时间毫秒左移22位
         */
        private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

        private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
        /**
         * 上次生产id时间戳
         */
        private static long lastTimestamp = -1L;
        /**
         * 并发控制
         */
        private long sequence = 0L;

        private final long workerId;
        /**
         * 数据标识id部分
         */
        private final long datacenterId;

        public Snowflake() {
            this.datacenterId = getDatacenterId(maxDatacenterId);
            this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
        }

        /**
         * @param workerId     工作机器ID
         * @param datacenterId 序列号
         */
        public Snowflake(long workerId, long datacenterId) {
            if (workerId > maxWorkerId || workerId < 0) {
                throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
            }
            if (datacenterId > maxDatacenterId || datacenterId < 0) {
                throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
            }
            this.workerId = workerId;
            this.datacenterId = datacenterId;
        }

        /**
         * 获取下一个ID
         *
         * @return
         */
        public synchronized long nextId() {
            long timestamp = timeGen();
            if (timestamp < lastTimestamp) {
                throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
            }

            if (lastTimestamp == timestamp) {
                // 当前毫秒内，则+1
                sequence = (sequence + 1) & sequenceMask;
                if (sequence == 0) {
                    // 当前毫秒内计数满了，则等待下一秒
                    timestamp = tilNextMillis(lastTimestamp);
                }
            } else {
                sequence = 0L;
            }
            lastTimestamp = timestamp;
            // ID偏移组合生成最终的ID，并返回ID
            long nextId = ((timestamp - twepoch) << timestampLeftShift)
                    | (datacenterId << datacenterIdShift)
                    | (workerId << workerIdShift) | sequence;

            return nextId;
        }

        private long tilNextMillis(final long lastTimestamp) {
            long timestamp = this.timeGen();
            while (timestamp <= lastTimestamp) {
                timestamp = this.timeGen();
            }
            return timestamp;
        }

        private long timeGen() {
            return System.currentTimeMillis();
        }

        /**
         * <p>
         * 获取 maxWorkerId
         * </p>
         */
        protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
            StringBuffer mpid = new StringBuffer();
            mpid.append(datacenterId);
            String name = ManagementFactory.getRuntimeMXBean().getName();
            if (!name.isEmpty()) {
                /*
                 * GET jvmPid
                 */
                mpid.append(name.split("@")[0]);
            }
            /*
             * MAC + PID 的 hashcode 获取16个低位
             */
            return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
        }

        /**
         * <p>
         * 数据标识id部分
         * </p>
         */
        protected static long getDatacenterId(long maxDatacenterId) {
            long id = 0L;
            try {
                InetAddress ip = InetAddress.getLocalHost();
                NetworkInterface network = NetworkInterface.getByInetAddress(ip);
                if (network == null) {
                    id = 1L;
                } else {
                    byte[] mac = network.getHardwareAddress();
                    id = ((0x000000FF & (long) mac[mac.length - 1])
                            | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
                    id = id % (maxDatacenterId + 1);
                }
            } catch (Exception e) {
                System.out.println(" getDatacenterId: " + e.getMessage());
            }
            return id;
        }
    }


}